In my opinion, spring is the best time to visit Japan. Spring is the best time to view Cherry Blossoms in Japan. Cherry blossoms are beautiful, and there are so many different types of cherry blossoms to experience. Japanese people love to go on a picnic called Hanami (花見) and celebrate the cherry blossom season.
Some people love to visit Japan in fall time to see the trees change colors, Kouyou (紅葉), but I think the weather is more beautiful and warmer in spring time. The day time gets longer, and there are different types of flowers blooming in different stages in the spring season. It’s just a happier time with everybody looking forward to the warmer season after the cold spells of winter.
I am from Hokkaido (北海道), the northernmost island of Japan, and spring comes later. Cherry blossoms bloom about 3-4 weeks later than Tokyo area . In my home town of Hakodate (函館) located in the Southern tip of Hokkaido, the cherry blossoms bloom in later April to early May.
Japanese love their cherry blossoms so much that there is always an up-to-date forecast of when the flowers are blooming in different locales each year. It is called Sakura Zensen (桜前線)-Cherry Blossom Front Line. For example, see Cherry blooming forecast 2016.
Last time I visited Hakodate in mid May 2016, the regular type of cherry blossoms were gone, but the later blooming type of blossoms (八重桜) were in full bloom.
Last time I visited Hakodate in mid-May of 2016, the regular type of cherry blossoms were all gone, but the later blooming type of blossoms (八重桜) were in full bloom.
I do not recommend a visit to Japan in summer time unless you are visiting only the northern parts of Japan. In Tokyo and in the southward, it gets extremely hot in the summertime especially in August. On top of the heat, the 90% humidity will get to you. I have been to tropical countries like Vietnam and Hong Kong, and August in Tokyo feels as hot or even hotter! I think it is compounded by all the buildings, cars and people in the city. In Hokkaido, it is nice in summertime with sunshine and temperature around 25C (77F) high. It seldom gets above 30C (88F). The weather is also less humid (カラッとしてる）。
I also do not recommend going to Japan in the middle of the winter. The Tokyo area does not get extremely cold, and it seldom snows. You will need to wear heavy coats. If you are staying in hotels, it is not an issue, but a normal household does not have a central heating system (energy is expensive). It is very hard to get by for those of us spoiled by the heating systems in Western style homes. There is a humorous article on this topic in Japan Times, A winter’s tale.
In the northern part of Japan, the climate is very cold, and the newer homes are built with central heating systems. However, it is miserable to try to go to sightseeing in the middle of the frigid cold spell. The temperature often stays below freezing point (0C/32F). In early February, Sapporo Snow Festival is held with giant snow and ice sculptures are on display. If you like snow and do not mind cold temperature, you will have a lot of fun visiting the festival.
After comparing different seasons, I strongly recommend that you visit Japan in the springtime. It has the best weather in my opinion and you get the added benefit of the beautiful cherry blossoms.